> Again, this is an exceptional event, so it's not worth investing too much developer time into.
I have to disagree here. Exceptional events are exceptionally important here, since so much progress is hidden from the user. It is absolutely critical to inform the user of what happened, so their expectations aren't broken, and to cleanly recover so the application is not in an incorrect state. I think this is the most important thing to invest developer time into in an application built in this way. Otherwise, you'll lose customer confidence do to unexpected behavior or even lost/corrupted data.
> Again, this is an exceptional event, so it's not worth investing too much developer time into.
I have to disagree here. Exceptional events are exceptionally important here, since so much progress is hidden from the user. It is absolutely critical to inform the user of what happened, so their expectations aren't broken, and to cleanly recover so the application is not in an incorrect state. I think this is the most important thing to invest developer time into in an application built in this way. Otherwise, you'll lose customer confidence do to unexpected behavior or even lost/corrupted data.